# Homework Help: Work Problem (Chin Ups)

1. Nov 6, 2009

### Chandasouk

1. The problem statement, all variables and given/known data

While doing a chin-up, a man lifts his body 0.40 m.

2. Relevant equations

Us = mgh
W = Fd

a) How much work must the man do per kilogram of body mass?

b)The muscles involved in doing a chin-up can generate about 70 J of work per kilogram of muscle mass. If the man can just barely do a 0.40-m chin-up, what percentage of his body's mass do these muscles constitute? (For comparison, the total percentage of muscle in a typical 70-kg man with 14% body fat is about 43%.)

c)Repeat part (b) for the man's young son, who has arms half as long as his father's but whose muscles can also generate 70 J of work per kilogram of muscle mass.

I have no clue how to begin. It seems they only provided me with $$\Delta$$X = .40m

2. Nov 6, 2009

### tiny-tim

Hi Chandasouk!

(have a delta: ∆ )
Yes, they have … they've also provided you with the mass (because everything is per kilogram).